Alkylpolyglycosides have been widely disclosed in the art as environmentally friendly carbohydrate-derived nonionic surfactants, and are used in various detergent and personal care products. Disclosures in the prior art include EP 75 995A (Procter & Gamble), EP 238 638B (Staley/Henkel), EP 487 262A (Unilever) and EP 374 702 A (Kao).
These materials are currently supplied as aqueous pastes containing only about 50 wt % of active matter, the balance being water. The water is present as a result of the manufacturing process, and is also important as a medium for the subsequent hydrogen peroxide bleaching step which is always required in order to obtain a light-coloured product. For example, EP 306 650A (Hals AG) discloses a process for the preparation of alkylpolyglycosides by glycosidation in alcoholic solution, followed by purification with active charcoal, removal of the alcohol by distillation, addition of further water, and bleaching with hydrogen peroxide. The product is an aqueous paste having an active matter content of about 50 wt %.
The aqueous paste possesses a number of disadvantages. Viscosity is too high for processability at 20.degree. C. and heating to 30.degree. C. or above is required. If the water is surplus to the requirements of the final detergent product, it must be removed by the detergent manufacturer either before or during its incorporation.
Traditional low- and medium-density detergent powders were and are prepared by spray-drying an aqueous slurry of all ingredients that are sufficiently heat-insensitive. This is a high temperature process in which large amounts of water are driven off. In this process the water associated with the polymer is a minor contributor to the total slurry moisture and makes little or no difference to the efficiency or energy consumption of the process.
The compact or concentrated powders which now form a substantial part of the market, however, are prepared by non-tower mixing and granulation processes which generally avoid high-temperature processing where water will be driven off. In such processes it is generally desirable that the moisture content should be kept as low as possible, both to facilitate granulation, which requires a carefully controlled balance of liquid and solid ingredients, and to ensure that the final product also has as low as possible a moisture content. Low moisture content is especially important for compositions to which moisture-sensitive bleach ingredients, especially sodium percarbonate, are to be added.
Mixing and granulation may be followed by a separate drying step, for example, in a fluidised bed, but that requires additional plant and the expenditure of additional energy.
Accordingly, for the preparation of compact high bulk density powders of low moisture content, the incorporation of alkylpolyglycosides in the form of aqueous pastes is not ideal.
The present inventors have now succeeded in preparing alkylpolyglycosides in a mobile, processable form having low water content, as blends with ethoxylated nonionic surfactants and strictly controlled amounts of water. The blends may readily be mixed and granulated with detergent solids by non-spray-drying processes to form particulate detergent compositions or components of high surfactant content and low water content, no further drying step being required.